I received yesterday a new company phone and was now challenged with the migration of my contacts from a Maemo5 system (Nokia N900) to a Windows 7.5 "Mango" system (Nokia Lumia 800). After some search in the internet I only found some documents/postings from people who made this over a way similar to "Nokia OVI software -> Windows -> CSV -> Import to Hotmail/Gmail/whatever -> Sync from mail provider to the phone" (Sync using Gmail and Sync using Hotmail) . Unfortunately, in the first step, I lost a lot of phone numbers due the created vcf files in the Windows folder are incomplete.

So I searched for a different option and found one

The new Windows system, offers a option/application called "Contacts Transfer". Unfortunately, to use this function your phone needs to support the Bluetooth PBAP protocol, which the Maemo phone doesn't do out of the box.

Prepare the N900:
1. Install a root shell http://wiki.maemo.org/Root_access#rootsh
2. Download the packages obexd2_0.37-0maemo1_armel.deb and libopenobex2-1.5-0maemo3_armel.deb from http://wiki.maemo.org/Bluetooth_PBAP#Installation_Guide with Firefox.
3. Open a X-terminal and type in "sudo gainroot" to open a root shell (will only work if step 1 was successful).
4. Move your working directory to the downloads directory of Firefox (per default "cd MyDocs/.documents/").
5. Install the packages, using the Debian packet manager. Command: "dpkg -i obexd2_0.37-0maemo1_armel.deb libopenobex2-1.5-0maemo3_armel.deb" If you receive a message from dpkg saying the working area is looked, restart the phone and continue from step 3.
6. Restart the phone. Fastest way for me, just type "reboot" in the X-terminal.

And now, your N900 is PBAP ready

Enable Bluetooth on your N900 and make it visible. Start the "Contacts Transfer" tool on your Lumia 800, if Bluetooth is disabled, it will ask for enabling it, so do it. It should find your N900 and you can connect the phones after you agreed on both phones.